Mineralized fast-growing wood composite material and preparation method thereof

Abstract

The invention relates to a mineralized fast-growing wood composite material and a preparation method thereof, and belongs to the technical field of wood modification. The preparation method of the mineralized fast-growing wood composite material comprises the following steps: (1) pretreating untreated poplar; (2) performing vacuum impregnation in a polycation solution; (3) performing vacuum impregnation in a polyanion solution; (4) performing vacuum impregnation in the polycation solution again; (5) adjusting the pH value of the precursor solution to 2-3, magnetically stirring, and then dipping in the precursor solution; (6) cleaning the surface with deionized water, air-drying, and drying in a drying oven until the surface is absolutely dry; and (7) repeating the steps (2)-(6) for several times. According to the modification method, the physical and mechanical properties of the poplar can be improved, the flame retardant property of the poplar can be remarkably improved, and new possibility is provided for high value-added application of the poplar.

Description

Technical Field

[0001] This application relates to the field of wood modification technology, and in particular to a mineralized fast-growing wood composite material and its preparation method. Background Technology

[0002] With global population growth and accelerated industrialization, the demand for environmentally friendly materials is increasing. Wood is an abundant, renewable, and structurally ordered natural organic biomass material. As a renewable natural resource, wood is widely used in construction, furniture, and packaging due to its biodegradability, aesthetic appeal, and excellent physical and mechanical properties. However, with the rapid development of the timber industry and the introduction of policies restricting the development of natural forest resources, timber resources are facing a shortage. Developing plantations can effectively alleviate the supply-demand imbalance. Poplar plantations are one of the most important fast-growing plantation species globally, mainly planted in China, Western Europe, and North America. Due to its relatively soft wood, fast growth rate, and short crop rotation cycle, poplar has become an important economic resource, primarily used to meet the growing demand for timber. However, fast-growing poplar has a loose texture, poor physical, mechanical, and flame-retardant properties, and is prone to decay and deformation, making it difficult to use directly, which limits the development of the timber industry. Therefore, functional improvement of fast-growing timber to enhance its key performance indicators has become an active area of ​​research in materials science. Wood modification typically employs physical, chemical, or combined physical-chemical methods to improve its properties, including dimensional stability, mechanical strength, corrosion resistance, flame retardancy, and acid and alkali resistance, thereby achieving high-value utilization of fast-growing timber. Modification of fast-growing timber mainly includes heat treatment, compression, resin impregnation, chemical grafting, wood mineralization, and nanoparticle modification, each with its own advantages. Among these, wood mineralization and compression, as wood reinforcement modification technologies, are highly efficient and environmentally friendly, with significant practical and social benefits, fully leveraging the resource advantages of fast-growing timber. The mechanical strength of wood is positively correlated with its density; therefore, increasing the density of fast-growing timber can improve its strength. Tissue densification technology improves the physical and mechanical properties of wood by increasing its density, offering advantages such as environmental friendliness, high efficiency, and the ability to utilize materials in their original state. Depending on the densification method, tissue densification technology can be divided into compression densification, impregnation densification, and a combination of compression and impregnation densification. Compression densification technology involves pre-treating the wood with heat softening without damaging the cell wall structure, and then using mechanical methods to compress the cell cavity volume for physical modification. Biomineralization is a common phenomenon in nature, as seen in pearls, shells, and bones. These biomineralized structures not only possess excellent mechanical properties but also exhibit high diversity and complexity in structure and function. The structural characteristics and mineralization mechanisms of these natural mineralized composite materials provide inspiration and theoretical basis for biomimetic mineralization design and synthesis. Therefore, biomimetic mineralization technology is considered an environmentally friendly method for synthesizing wood nanomaterials, capable of synthesis under mild conditions and characterized by low energy consumption and non-toxicity. In recent years, researchers have used chitosan with biomimetic mineralization functions to perform multilayer self-assembly with SiO2 to synergistically modify wood through biomimetic mineralization. This method has successfully improved the properties of eucalyptus wood, enhancing its compressive strength along the grain, impact toughness, and abrasion resistance.In preparing these composite materials, a common method is to use vacuum impregnation and pressure techniques to effectively integrate silica sol into the wood. The mass and quantity of SiO2 gel in the composite material increase with prolonged impregnation time. This process typically preserves the cellular structure of the wood and promotes the formation of covalent bonds between the -OH groups of the wood and the silica sol, thereby generating Si-O-Si and Si-OC bonds. This significantly improves the thermal and physical properties of the prepared composite material, making it more suitable for various applications. Inspired by natural wood, some scholars have proposed a biomimetic strategy to prepare hydrogel composite materials with high anisotropy, ultra-high strength, high stiffness, and osteoconductivity. This technique is achieved by impregnating biocompatible materials into delignified wood, followed by in-situ mineralization of hydroxyapatite nanocrystals. Fu et al. (2019) prepared a multi-level reinforcing material containing carbon fibers, SiO2, and graphene by coating SiO2 and graphene onto the surface of carbon fibers through layer-by-layer electrostatic self-assembly. After assembly with SiO2 / graphene, the surface roughness and wettability of the resulting material are improved, thus forming a strong mechanical interlock with the resin. Bi et al. (2023) proposed a layer-by-layer self-assembly-based method to enhance the interfacial compatibility between fiber-reinforced poly(3-hydroxybutyrate) and bamboo fiber. Using sodium lignin sulfonate derived from pulp and paper industry waste as raw material, long carbon chains were introduced into sodium lignin sulfonate through the Mannich reaction, thereby forming a hydrophobic self-assembled multilayer structure on the surface of bamboo fiber. These modifications effectively improved the mechanical properties of the composite material. Liu et al. (2023) successfully developed a hybrid wood composite material with both high strength and excellent flame retardant properties by adopting a combined strategy of delignification, mineralization, and densification. The delignification process promoted the deposition of minerals inside the wood, while the mineralization process significantly improved the properties of the wood.

[0003] In summary, multilayer self-assembled mineralized wood is typically achieved by constructing a biomineralization microenvironment. This process requires analyzing the interfacial structures, such as the bonding types between the organic and inorganic matrices, the surface structure of the organic matrix, and the covalent bonds and electrostatic interactions between inorganic crystals. Furthermore, the electrostatic interactions between charged groups on the organic matrix surface and inorganic ions, as well as the morphology of inorganic minerals, should be investigated. Ultimately, the research focuses on the recognition and regulation of organic macromolecules in wood mineralization and the evaluation of various performance indicators of the composite material. Summary of the Invention

[0004] In view of this, this application provides a mineralized fast-growing wood composite material and its preparation method, which can effectively overcome the defects of the prior art.

[0005] The first aspect of this application provides a method for preparing a mineralized fast-growing wood composite material, comprising the following steps:

[0006] (1) Immerse the untreated poplar wood in deionized water at room temperature and pressure to remove impurities from the surface of the poplar wood; then take out the poplar wood and dry it until it is completely dry for later use; then immerse the poplar wood in an alkaline solution at room temperature and pressure, and then wash the surface of the poplar wood with deionized water.

[0007] (2) The treated poplar wood was placed in a polycationic solution for vacuum impregnation and the surface of the poplar wood was cleaned;

[0008] (3) The poplar wood that has been impregnated with the polycationic solution is then placed in the polyanionic solution for vacuum impregnation, and the surface of the poplar wood is cleaned.

[0009] (4) Then the sample is immersed in the polycationic solution again for vacuum impregnation and the poplar surface is cleaned;

[0010] (5) Prepare a precursor solution by mixing silicon source with deionized water, adjust the pH of the solution to 2-3, stir magnetically, and then pressurize and impregnate the poplar wood treated in step (4) into the precursor solution;

[0011] (6) Remove the poplar wood from the SiO2 precursor solution, wash the surface with deionized water, air dry it, and then put it into an oven to dry it completely.

[0012] (7) Repeat steps (2), (3), (4), (5) and (6) several times to prepare mineralized fast-growing wood composite material.

[0013] It should be noted that repeating steps (2), (3), (4), (5) and (6) once results in a single layer of mineralized fast-growing wood composite material, repeating it twice results in a double layer of mineralized fast-growing wood composite material, repeating it three times results in a triple layer of mineralized fast-growing wood composite material, and so on.

[0014] Fast-growing timber species refer to tree varieties that grow quickly, mature early, and have short rotation periods, such as poplar, eucalyptus, fir, paulownia, and willow. Timber made from these fast-growing species is called fast-growing timber. It is typically softer and has poorer physical and mechanical properties, flame retardancy, and corrosion resistance. It is generally used for papermaking, construction, and as core material for boards, and some is also used in furniture manufacturing, but all require modification treatment.

[0015] This application focuses on fast-growing poplar (and similar fast-growing timbers such as eucalyptus and fir). Utilizing the principle of biomimetic mineralization, it combines layer-by-layer (LBL) self-assembly with the sol-gel method to construct a multilayer self-assembled SiO2 mineralized fast-growing timber composite material. The LBL method is an environmentally friendly surface material preparation method. Its unique environmental response characteristics give it application potential for preparing functional materials and thin films. It relies on utilizing various forces (electrostatic effects, hydrogen bonds, and coordination bonds) to induce particle adsorption and the formation of multilayer structures. Alternating deposition of polyelectrolyte layers with opposite charges on various substrate surfaces forms a stable organic-inorganic hybrid structure. The sol-gel method, on the other hand, is a wet chemical method that generates inorganic materials in situ on the substrate surface by controlling chemical reactions in a solution. Combining these two methods not only allows for the construction of organic layer films on the wood surface, providing nucleation sites for inorganic nanoparticles, but also enables the in-situ mineralization of SiO2 on the wood cell walls, forming an organic-inorganic hybrid structure, thereby improving the flame retardancy and mechanical properties of the wood. The advantages of multilayer self-assembly technology are its simplicity, lack of need for complex instruments or equipment, affordable materials, rapid reaction, minimal damage to the matrix and surface structure, and controllability of the assembly of each layer within the structure. The porous structure of wood provides an excellent space for in-situ SiO2 mineralization, and the active hydroxyl groups (-OH) on the wood surface offer favorable conditions for electrostatic adsorption and chemical cross-linking with chitosan and SiO2.

[0016] This application, based on the principle of biomineralization, employs a room-temperature vacuum pressure impregnation process for wood, combining a multilayer self-assembly method and a sol-gel method to prepare and characterize a multilayer self-assembled SiO2 mineralized fast-growing wood composite material. Specifically, the process involves cyclically impregnating wood in polycationic and polyanionic solutions using a multilayer self-assembly method. This constructs an organic coating film on the wood cell walls, providing nucleation sites for inorganic nanoparticles, enabling SiO2 to rapidly deposit and directionally crystallize within the cell walls and intercellular spaces. By introducing chitosan, an organic inducing agent providing nucleation sites for SiO2, and considering its film-forming properties and good biocompatibility, a chitosan-SiO2 film can be formed on the mineralized wood cell walls, further improving the wood's properties, including flame retardancy and physical and mechanical properties. This modification method not only enhances the physical and mechanical properties of poplar but also significantly improves its flame retardancy, providing new possibilities for high-value-added applications of poplar. Through in-depth research on this preparation process and performance evaluation, a new strategy for high-value utilization of low-value fast-growing poplar and enhancing the interfacial compatibility of biocomposite materials is proposed, providing scientific basis and technical support for the functional modification of biomass materials and the development of environmentally friendly materials.

[0017] Preferably, in step (1), the immersion time in deionized water is 24 h.

[0018] Preferably, in step (1), the immersion time in the alkaline solution is 15 min, and the alkaline solution is a 2% NaOH solution by mass.

[0019] Preferably, in steps (2) and (4), the polycationic solution is selected from chitosan, polydiallyldimethylammonium chloride, polyethyleneimine, and polyacrylamide hydrochloride, and the concentration of the polycationic solution is 8 g·L⁻¹. -1 .

[0020] Preferably, in steps (2), (3) and (4), the specific conditions for vacuum impregnation are: negative pressure of 0.1 MPa, impregnation time of 1 h, and impregnation temperature of 20 ℃.

[0021] Preferably, in step (3), the polyanionic solution is selected from one of sodium polystyrene sulfonate, sodium phytate, polyacrylic acid, and sodium alginate, and the concentration of the polyanionic solution is 5 g·L. -1 .

[0022] Preferably, in step (5), the silicon source and deionized water are in a mass ratio of 5:1.

[0023] Preferably, in step (5), the magnetic stirring time is 30 min.

[0024] Preferably, in step (5), the time for pressurized immersion in the precursor solution is 12 h, and the pressure is maintained at 0.5 MPa.

[0025] The second aspect of this application also provides a mineralized fast-growing wood composite material, which is prepared by the above method.

[0026] Compared with the prior art, this application has the following advantages:

[0027] This application responds to the growing global demand for environmentally friendly materials. Using fast-growing poplar as the substrate, a chitosan-coated SiO2-mineralized fast-growing wood composite (LSP) was successfully prepared by combining biomimetic mineralization principles with a multilayer self-assembly (LBL) method and a sol-gel method. The study first pretreated the poplar to remove surface impurities and activate hydroxyl groups. Then, chitosan and sodium polystyrene sulfonate were alternately deposited using LBL technology to construct a multilayer organic film, providing nucleation sites for SiO2. Subsequently, SiO2 was mineralized in situ on the poplar cell walls using the sol-gel method, forming an organic-inorganic hybrid structure to improve the flame retardancy and mechanical properties of the poplar. Characterization results show that the oven-dry density of the prepared composite material is 0.42 g·cm³. -3 Increased to 0.53 g·cm³ -3The weight gain was 12.54%, and the water resistance was significantly improved. The radial saturated water swelling rate decreased to 0.41%, the tangential saturated water swelling rate decreased to 8.14%, the volumetric saturated water swelling rate decreased to 2.01%, and the 24-hour water absorption rate decreased to 40.45%. Infrared spectroscopy analysis showed the formation of Si-O-Si and Si-OC bonds, confirming the chemical bonding of SiO2 with the poplar cell wall. Scanning electron microscopy observed the uniform distribution of nano-sized SiO2 on the poplar cell wall. Thermogravimetric analysis results showed that the composite material's T... 5% and T 10% The value decreases, T max The thermal stability of the composite material was significantly improved, with the thermal value decreasing from 363 °C to 344 °C and the char residue at 800 °C increasing from 13.49% to 20.53%. This application provides a new strategy for the high-value-added application of low-value fast-growing poplar and offers scientific basis and technical support for the functional modification of biomass materials and the development of environmentally friendly materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 A process flow diagram for the preparation of mineralized fast-growing wood composite materials;

[0030] Figure 2 Diagrams illustrating the electrostatic adsorption and chemical reaction mechanisms during the preparation of mineralized fast-growing wood composite materials;

[0031] Figure 3 FTIR spectra of CK and LSP;

[0032] Figure 4 Thermogravimetric (TG) and differential thermogravimetric (DTG) curves for CK and SDP;

[0033] Figure 5 SEM images of CK (A. cross section, B. chord section);

[0034] Figure 6 SEM-EDS images of LSP (A. cross section, B. chord section, C. EDS layered image, D~F. EDS spectrum, G. elemental content). Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Unless otherwise specified, the experimental methods used in the embodiments of this application are all conventional methods.

[0037] In the following examples, unless otherwise specified, all raw materials can be obtained by commercial purchase or conventional methods.

[0038] 1. Materials and Methods

[0039] 1.1 Materials and Instruments

[0040] 1.1.1 Materials and Reagents

[0041] This application uses fast-growing plantation poplar (P. euramevicana) wood from Siyang County, Suqian City, China as the test material. Poplar samples of different sizes were prepared according to relevant testing standards for the physical and mechanical properties of wood. Main chemical reagents: Sodium hydroxide (NaOH), AR, 96%, Shanghai Aladdin Chemical Reagent Co., Ltd.; Hydrochloric acid (HCl), analytical grade GR, 36%~38%, Shanghai Aladdin Chemical Reagent Co., Ltd.; Tetraethyl orthosilicate (TEOS, C8H2O). 20 O4Si), SiO2 purity >28%, Shanghai Aladdin Chemical Reagent Co., Ltd.; Chitosan (CS, C 56 H 103 N9O 39 ), deacetylation degree 90%, Shanghai Aladdin Chemical Reagent Co., Ltd.; acetic acid (CH3COOH), AR, Sinopharm Chemical Reagent Co., Ltd.; sodium polystyrene sulfonate (PSS, (C8H7NaO3S)n), AR, 98%, Sinopharm Chemical Reagent Co., Ltd.

[0042] 1.1.2 Main Instruments and Equipment

[0043] Vacuum high-pressure impregnation tank: AF-5, Dongguan Chenrui Precision Technology Co., Ltd.; Air compressor / pump: 3190W-35L, China Yangzi Group Chuzhou Yangzi Air Conditioner Co., Ltd.; Low-voltage electrostatic field equipment: Bx2000, Zhejiang Chili Technology Co., Ltd.; Portable spectrophotometer (colorimeter): DS-210, Hangzhou Caipu Technology Co., Ltd.; Gloss meter: YG60, Shenzhen Sanenshi Technology Co., Ltd.; Contact angle meter: CA200, Kunshan Beidou Precision Instrument Co., Ltd.; Fourier transform infrared spectrometer: Nicolet iS20, Thermo Fisher Scientific Inc. (China); Thermogravimetric analyzer: Netzsch TGA209F1, NETZSCH GmbH, Germany. The matching crucible material is Al2O3, with a capacity of 0.06 mL; Scanning electron microscope: ZEISS Sigma300; X-ray energy dispersive spectrometer: Oxford Xplore 30, Zeiss GmbH, Germany.

[0044] 1.2 Preparation method and mechanism of multilayer self-assembled SiO2 mineralized fast-growing wood composite material

[0045] The preparation process of multilayer self-assembled chitosan-co-SiO2 mineralized fast-growing wood composite material is as follows: (1) Untreated poplar wood is immersed in deionized water at room temperature and pressure for 24 h to remove impurities from the surface of the poplar wood. Then the poplar wood is taken out and dried to dryness for later use. Next, the poplar wood is immersed in a 2% NaOH solution at room temperature and pressure for 15 min, and then the surface of the poplar wood is washed with deionized water. (2) The treated poplar wood is placed in an 8 g·L -1 Vacuum impregnation in chitosan solution for 1 h (negative pressure 0.1 MPa, temperature 20 ℃), then cleaning the poplar surface. (3) Place the poplar impregnated in chitosan solution into a 5 g·L⁻¹ container. -1 The sample was vacuum impregnated in a sodium polystyrene sulfonate solution for 1 h (negative pressure 0.1 MPa, temperature 20 ℃) ​​and the poplar surface was cleaned. (4) Then the sample was placed in an 8 g·L solution again. -1(5) Vacuum impregnation in chitosan solution for 1 h (negative pressure 0.1 MPa, temperature 20℃), and cleaning of poplar surface. (6) Prepare SiO2 precursor solution by mixing TEOS and deionized water at a mass ratio of 5:1, and use hydrochloric acid as catalyst to adjust the pH of the solution to 2~3. After preparing the solution, stir under magnetic stirring for 30 min, and then impregnate the above-treated poplar in SiO2 precursor solution under pressure for 12 h, with the pressure maintained at 0.5 MPa. (7) Take the poplar out of SiO2 precursor solution, clean the surface with deionized water, air dry, and then put it in an oven to dry completely. (8) Repeat the above steps (2), (3), (4), (5), and (6) twice to prepare a three-layer chitosan-co-SiO2 mineralized fast-growing wood composite material, labeled as LSP. Its preparation process is as follows. Figure 1 As shown.

[0046] Untreated poplar wood was immersed in deionized water at room temperature and pressure for 24 hours to remove impurities from the surface of the poplar wood, and then dried to absolute dryness to obtain the CK group.

[0047] The technical mechanism of multilayer self-assembled SiO2 mineralized fast-growing wood composite material: Poplar wood samples are alternately impregnated in polyelectrolyte solutions with opposite charges. Utilizing the principle of electrostatic adsorption, the two polyelectrolytes with different charges are bound together in an orderly and tight manner. Through repeated alternating impregnation, a self-assembled organic film layer of polyelectrolytes can be obtained on the surface of the poplar wood samples. Based on the principle of biomimetic mineralization, the interaction between the organic matrix and inorganic mineral nucleation growth is utilized. Combined with the multilayer self-assembly method, multiple organic films are assembled on the surface of the poplar wood samples, thus providing nucleation sites for inorganic minerals and offering a new approach and pathway for poplar wood mineralization. The electrostatic adsorption mechanism and chemical reaction mechanism in the preparation process of multilayer self-assembled SiO2 mineralized fast-growing wood composite material are as follows: Figure 2 As shown.

[0048] 1.3 Performance Testing and Characterization

[0049] 1.3.1 Weight Gain Percentage (WPG)

[0050] Before treatment, 20 mm × 20 mm × 20 mm (R × T × L) poplar specimens were dried to absolute dryness and weighed. After mineralization was completed, they were dried to absolute dryness and weighed again. The weight gain rate of the specimens was calculated.

[0051] (1)

[0052] Where: M1 is the oven-dry weight of poplar wood in the blank control group, in g;

[0053] M2 is the oven-dry mass of the poplar wood after mineralization treatment, in grams;

[0054] 1.3.2 Oven-dry density

[0055] Referring to the standard GB / T 1927.5-2021 "Test Methods for Physical and Mechanical Properties of Wood in Small, Defect-Free Samples - Part 5: Determination of Density", 20 mm × 20 mm × 20 mm (R × T × L) specimens were dried to absolute dryness, weighed, and the density of the specimens was calculated.

[0056] (2)

[0057] Where: ρ is the density of the specimen when it is completely dry, in g·cm³ -3 ;

[0058] M is the mass of the specimen when it is completely dry, in grams;

[0059] V is the volume of the specimen, in cm³ 3 ;

[0060] 1.3.3 Saturated water swelling

[0061] Referring to standard GB / T 1927.8-2021 "Test Methods for Physical and Mechanical Properties of Wood in Defect-Free Small Samples - Part 8: Determination of Wetting Swelling", the dimensions of the samples were measured in both the oven-dry and saturated water states, and the radial saturated water swelling rate (α) was determined. rs ), tangential saturated water swelling ratio (a ts ) are calculated according to formula (3) and formula (4) respectively.

[0062] (3)

[0063] (4)

[0064] In the formula: a rs and a ts The saturated water swelling ratios are the radial and tangential directions, respectively; L rs and L ts The radial and tangential dimensions, respectively, are when the moisture content of the sample is higher than the fiber saturation point (i.e., saturated water), in mm; L ro and L to These are the radial and chordal dimensions of the sample when it is completely dry, in mm.

[0065] When the sample changes from completely dry to saturated with water, the volumetric swelling rate due to water saturation is calculated according to formula (5) when considering the dimensional changes along the grain.

[0066] (5)

[0067] In the formula: a vs L is the saturation swelling ratio of the sample volume; rs L ts and L hsThe dimensions (in mm) are the radial, tangential, and longitudinal dimensions of the sample when the moisture content is above the fiber saturation point (i.e., saturated). r0 L t0 L h0 These are the radial, tangential, and longitudinal dimensions (mm) of the sample when it is completely dry.

[0068] 1.3.4 Water Absorption Rate

[0069] Referring to national standard GB / T 1934.1-2021, 20 mm × 20 mm × 20 mm (R × T × L) specimens were dried to absolute dryness and weighed. They were then immersed in deionized water, pressed down to at least 50 mm below the water surface, and weighed again after 24 hours. The water absorption rate was calculated using the following formula:

[0070] (6)

[0071] Where: A is the water absorption rate of the specimen, %

[0072] M1 is the mass of the specimen when it is completely dry, in grams;

[0073] M2 is the mass of the specimen after absorbing water, in grams;

[0074] 1.3.5 Surface color difference and gloss

[0075] An automatic colorimeter was used to determine the correlated colorimetric properties of the samples. The CIE (1976) standard was adopted. a b A color system represents color, where L For brightness, a and b These are the chromaticity indices for the red-green axis and the yellow-blue axis, respectively. The formula for calculating total color difference is:

[0076] (7)

[0077] In the formula, ΔL = L t - L0 ;Δa = a t - a0 ;Δb = b t - b0 L0, a0, b0 are specimens before mineralization, L ta t b t This represents the specimen after mineralization.

[0078] The formula for calculating the chromaticity value C:

[0079] (8)

[0080] Hue angle (H) o Calculate according to formula (9):

[0081] (9)

[0082] Surface gloss (G) The gloss intensity of wood surfaces is related to the tree species, surface smoothness, tyloses and inclusions, wood structural characteristics, and wood cross-section. This study used a gloss meter for measurement, primarily investigating the direction of light incident parallel to GZL (%) and perpendicular to GZT (%) along the grain direction. Multiple measurements were performed at multiple points on each sample (3 points, 3 measurements per point), with a measurement angle of 60°. The average value was taken as the measured value.

[0083] 1.3.6 Contact Angle

[0084] The specimens before and after mineralization treatment were dried in a 105 ℃ electric thermostatic drying oven until the samples were completely dry before testing. All measurements were performed three times and the average value was calculated.

[0085] 1.3.7 Fourier Transform Infrared Spectroscopy (FTIR) Detection

[0086] All prepared sample powders were dried in an electrically heated constant-temperature drying oven at 105 °C for 12 h before testing. The particle size of the powder was below 200 mesh, and the spectral frequency was between 400 and 4000 cm⁻¹. -1 Within a range, at 4 cm -1 The resolution was obtained by performing 15 scans to analyze the chemical structure of mineralized poplar.

[0087] 1.3.8 Scanning Electron Microscopy (SEM) Detection

[0088] The SEM was equipped with an energy-dispersive X-ray analyzer (EDX) to treat all samples with platinum to increase their conductivity. The measurement voltage was 20 kV to observe the microstructure of the mineralized poplar composite.

[0089] 1.3.9 Thermogravimetric analysis (TG) test

[0090] Thermogravimetric analyzer: Model STA449F5 automatic sample-injection simultaneous thermal analyzer, manufactured by NETZSCH. The crucible material was Al2O3, with a capacity of 0.06 mL. All sample powders were dried in a 105 °C forced-air drying apparatus for 12 h before testing. The particle size of the sample powder was below 40–60 mesh. The two types of samples were placed separately into the Al2O3 crucible of the thermal analyzer and tested at 60 mL / min. -1 Nitrogen atmosphere, at 10 °C·min -1 The heating rate of the test samples was measured, and the temperature was increased to a range of 30–800 °C to analyze the thermal stability of the mineralized poplar. 5% T 10% These represent the temperatures at which the weight decreases by 5% and 10%, respectively. (DTG) max T represents the maximum weight loss during the entire pyrolysis process. max The value indicates the corresponding temperature. The carbon residue rate at 800 ℃ indicates the residual mass of the sample at 800 ℃.

[0091] 2 Results and Discussion

[0092] 2.1 Dimensional stability analysis

[0093] Table 1. Differences in dimensional stability-related indices between CK and LSP

[0094]

[0095] Note: CK is the control sample, and LSP is a multilayer self-assembled chitosan-co-SiO2 mineralized fast-growing wood composite material.

[0096] Compared to CK, the oven-dry density of LSP increased to 0.53 g·cm³. -3 The weight gain rate was 12.54%, a rs a ts a vsThe water absorption rates of CK and LSP were significantly reduced (Table 1). The 24-h water absorption rates were 84.77% and 40.45%, respectively. This indicates that poplar is a material with good water absorption, due to the large number of hydrophilic -OH groups on its surface. The natural porous structure of poplar not only endows it with low density and light weight but also provides ample storage space for moisture. However, this also leads to dimensional instability and susceptibility to natural degradation. Modification of poplar mainly involves reducing the -OH groups on its surface, which not only reduces water absorption but also improves dimensional stability. -OH groups, as active groups, are suitable as reaction binding sites for modifiers. In this application, NaOH is used to activate the poplar surface, making it negatively charged and allowing it to adsorb positively charged CS solution. The improvement in the dimensional stability of LSP is mainly due to the formation of unstable orthosilicic acid during the hydrolysis of TEOS. Orthosilicic acid undergoes a dehydration condensation reaction with the -OH groups on the poplar surface, resulting in the in-situ generation of SiO2 particles in the poplar cell walls or cavities. These particles fill the pores of the poplar, ultimately hindering water impregnation and penetration, thus reducing water absorption. Furthermore, through multilayer self-assembly, an organic-inorganic hybrid structure is constructed on the poplar surface. SiO2 forms chemical bonds with active groups on the poplar cell walls, consuming some hydrophilic groups and further reducing the water absorption of the poplar surface. The results of this application are consistent with the findings of Liu et al. (2020), indicating that specific chemical treatments can significantly reduce the water absorption of poplar. This application also examined more relevant dimensional stability indicators, further revealing the effect of SiO2 mineralization on improving the dimensional stability of poplar.

[0097] 2.2 Differences in surface color and gloss

[0098] Table 2. Changes in surface color and gloss of CK and LSP

[0099]

[0100] This application conducted a detailed analysis of the surface color and gloss of SiO2-mineralized fast-growing wood composites to evaluate their effects on the aesthetics and functionality of poplar. Table 2 shows that the L* values ​​of the tangential section (CK) and LSP were higher than those of the corresponding transverse sections. Compared to CK, the L* values ​​of LSP decreased on both the transverse and tangential sections. This is likely due to the orderly deposition and directional crystallization of SiO2 on the poplar cell walls and pores, transforming the porous structure of poplar into a dense structure, thereby increasing its light absorption and leading to a lower L* value. Compared to CK, the a* and b* values ​​of LSP increased on both the transverse and tangential sections, indicating a shift in color towards red and yellow hues. This is because SiO2 covalently bonds with the active groups on the poplar cell walls, forming an organic-inorganic hybrid structure. This structure not only improves the mechanical and flame-retardant properties of poplar but also alters its optical properties. On the same cross-section, the C* value of LSP increased compared to CK. The total color difference (ΔE*) of LSP is greater on the cross section than on the tangential section, indicating that the color change of LSP is most significant on the cross section. Nano-SiO2 fills the pores, altering the microstructure of poplar and affecting light reflection and absorption, thus influencing the C* value. The numerous carbon-oxygen (C=O), carbon-carbon (C=C) conjugated double bonds, hydroxyl (-OH), and methoxy (-OCH3) chromophores or auxochromic groups present in poplar undergo chemical bond breakage and recombination under external conditions such as NaOH, O2, and drying, leading to changes in LSP color. The dense microstructure formed by SiO2 and poplar may alter the intensity of surface reflected light, thus causing changes in the G* value. Unlike the study by Bak et al. (2022) which showed significant darkening of samples due to in-situ polymerization of microporous SiO2 aerogels to modify poplar, this application employs a combination of multilayer self-assembly and sol-gel methods, which demonstrate unique effects in altering the surface color and gloss of poplar.

[0101] 2.3 Variation of surface contact angle

[0102] Table 3. Changes in contact angle-related parameters of poplar wood and self-assembled SiO2.

[0103]

[0104] Mineralization of biomass materials typically increases the contact angle of the resulting composite materials. To improve the hydrophobicity and moisture resistance of wood, researchers used tetraethoxysilane (TEOS) and methyltriethoxysilane as precursors to prepare hydrophobic coatings on the wood surface. Bi et al. (2023) used sodium lignin sulfonate extracted from pulp and paper industry waste as a raw material. Subsequently, long carbon chains were introduced into sodium lignin sulfonate via the Mannich reaction, thereby constructing a hydrophobic self-assembled multilayer structure on the surface of BFs. The results of this application are the opposite. According to Table 3, the contact angles of CK on the cross section and tangential section were 61.55° and 54.44°, respectively, while the contact angles of LSP decreased to 15.85° and 19.8°, respectively. In the same cross section, the contact angle of CK is larger than that of LSP because the expansion stress under vacuum during the preparation of LSP results in a uniform distribution of SiO2, with nano-SiO2 adhering to the poplar surface in the form of a film. This filling effect may smooth the microstructure of the poplar surface, thereby reducing the contact angle. Furthermore, during the preparation of LSP, separation occurs between the poplar cell walls, creating numerous pores. These pores result in many invisible voids and gaps on the mineralized poplar surface, leading to rapid moisture absorption by the LSP and a significant reduction in the contact angle. Surface free energy is an important indicator of the ability of a sample surface to interact with other substances. The highest surface free energy of LSP on the cross-section is 70.17 mJ·m. -2 The lowest surface free energy of CK on the cross-section is 46.9 mJ·m. -2 In the same cross-section, the surface free energy of LSP is higher than that of CK, indicating that the LSP surface has stronger adhesion and wettability, which is conducive to the adhesion of substances such as coatings and adhesives. In addition, the SiO2 particles on the LSP surface have a large number of -OH hydrophilic groups, resulting in a smaller water contact angle. In contrast, CK did not undergo NaOH solution pretreatment, which resulted in the -OH groups on its surface not being activated, and its hydrophilicity was lower than that of LSP.

[0105] In the actual production processes of wood gluing, finishing, and preservation, the hydrophilicity and surface free energy of the wood surface are key factors affecting properties such as gluing strength, coating adhesion, and preservative penetration. During the use of wood products, surface finishing is often used to enhance visual appeal and decorative effects, and extend the service life of the products. This study found that multi-layer self-assembled chitosan synergistic SiO2 mineralization treatment can reduce the initial contact angle of poplar and increase its surface free energy. During wood gluing, a lower contact angle and higher surface free energy facilitate the spreading and penetration of adhesives on the wood surface, thereby forming a better gluing interface and improving gluing strength. In terms of wood finishing, SiO2 mineralization treatment can significantly improve the surface properties of poplar, enhance the adhesion between coatings and modified poplar, and improve the durability and decorative effect of the coating. This application also has certain guiding significance for the development of new wood modification technologies and the optimization of wood processing technology, contributing to the development of wood science and technology and improving the utilization value of wood resources.

[0106] 2.4 Characterization and Analysis of FTIR

[0107] FTIR can clearly identify the chemical bonds and functional groups present in biomass materials, helping to understand the degree of chemical cross-linking between silica sol and poplar wood, which is crucial for improving the overall performance of LSP. From Figure 3 It can be seen that the main absorption peaks are concentrated at 460, 803, 848, 1059, 1163, 1233, 1735, 2844 and 3412 cm⁻¹. -1 CK is 3412 cm -1 The surrounding area contains a large number of -OH groups. Therefore, this study used NaOH to activate the -OH groups on the poplar surface, providing a large amount of negative charge to the poplar surface. Furthermore, compared to the control (CK), the functional groups (-OH) of the LSP showed a red shift, which may be due to the formation of hydrogen bonds between chitosan or SiO2 and the poplar. (1250 cm⁻¹) -1 The stretching vibration peaks of the nearby acyl-oxygen bonds (COOR) were significantly reduced, which may be due to the reaction between the amino groups (-NH2) on the chitosan side chains and the carboxyl groups (-COOH) on the poplar wood. 2844 cm⁻¹ -1 Nearby fatty acids (CH) and 1735 cm -1 The weakening of the stretching vibration peak of nearby lignin (C=O) is due to the formation of a ligand between -COOH in poplar and -NH2 in chitosan. (803 cm⁻¹) -1 and 1059 cm -1 The nearby Si-O-Si stretching vibration peak, and the 460 cm⁻¹ peak. -1The appearance of the stretching vibration peak of SiO2 nearby indicates that SiO2 has entered the interior of poplar. Another possibility is that SiO2 chemically bonds with -COOH on the poplar surface (Si-O-C), such as at 1163 cm -1 The appearance of the Si-O-C absorption peak nearby fully proves this point. The characteristic peak representing Si-CH3 at 848 cm in LSP -1 did not appear. This indicates that SiO2 constructs an organic-inorganic hybrid structure on the poplar surface, realizing the mineralization modification of poplar under the synergistic effect of chitosan and SiO2. Qu et al. (2021) used tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) as precursors and prepared a hydrophobic coating on the wood surface by sol-gel method and post-aging heat treatment method to enhance hydrophobicity and moisture resistance. The results of infrared spectroscopy analysis show that the coating has good heat resistance and improves the thermal stability of wood. The results of this application echo those of this study, and both found that the introduction of inorganic SiO2 nanoparticles can change the chemical structure of poplar. In addition, this application particularly emphasizes the influence of the mineralization treatment of chitosan and SiO2 on the characteristic peaks of the FTIR spectrum, and more chemical bond changes are shown on the FTIR spectrum.

[0108] 2.5 Thermal stability analysis

[0109] Table 4 Differences in thermogravimetric analysis indexes of CK and LSP

[0110]

[0111] Thermogravimetric analysis (TGA) is a key characterization method for evaluating the thermal stability of composites and can obtain the thermal degradation information of materials under heating conditions. As can be seen from Figure 4 and Table 4, compared with CK, the values of T 5% and T 10% of LSP both decreased. Combining with the DTG curve, it can be seen that the thermal degradation of poplar can be divided into three stages: the pyrolysis rate in the first stage (200 - 290 °C) is relatively low and the mass loss is large, mainly involving the partial pyrolysis of hemicellulose and lignin; the second stage (290 - 380 °C) is mainly due to the continuous degradation of lignin and cellulose. In the third stage (380 - 800 °C), the remaining poplar components continue to undergo aromatization and carbonization until finally pyrolyzed into ash. Compared with CK (T max = 363 °C), the T maxThe value was lowered to 344℃, indicating that SiO2 in LSP effectively reduced the peak value of DTG. This is mainly because SiO2 particles generated during the hydrolysis and condensation of TEOS form hydrogen bonds with the poplar surface. The SiO2 particle surface contains a large number of -OH groups, which can also chemically bond with a small amount of -COOH on the poplar surface, forming an organic-inorganic hybrid structure. This result is consistent with the FTIR analysis. Furthermore, by controlling the molecular network between the polycationic electrolyte and the polyanionic electrolyte through multilayer self-assembly, the compatibility between poplar and inorganic particles can be effectively improved. By measuring the weight loss during temperature changes, researchers can determine the thermal degradation behavior of mineralized modified poplar compared to the control sample. According to Farzadi et al. (2019), the thermal stability of poplar can be significantly improved by introducing inorganic nanoparticles. The results of this study are consistent with this; thermogravimetric analysis (TGA) shows that the thermal stability of LSP is enhanced compared to the control sample. max The value decreased, and the char content at 800 °C increased. In the study by Ren et al. (2017), the thermal stability of poplar was improved through chemical modification. This application further found that after chitosan-synergistic SiO2 mineralization treatment, the thermal stability of poplar not only improved, but also the maximum weight loss (DTG) during pyrolysis was reduced. max The pyrolysis rate of poplar wood also decreased, indicating that the introduction of SiO2 particles helped to slow down the pyrolysis rate of poplar wood.

[0112] 2.6 Microscopic Morphology and Organization Analysis

[0113] Analyzing the microstructure of composite materials using techniques such as SEM-EDS can reveal the interaction between silica sol and poplar fiber. Figure 5 This is an SEM image of a control sample of poplar wood without any treatment, combined with... Figure 5 and Figure 6 It is known that chitosan provides a large number of nucleation sites for SiO2. The LSP prepared after three cycles of mineralization contains a large number of nano- and micro-sized SiO2 on its surface, forming an organic-inorganic hybrid structure on the poplar cell wall. This indicates that with the increase of the number of self-assembled layers, positively charged chitosan and negatively charged silica sol form an interpenetrating film layer due to electrostatic adsorption. The main mechanism is that chitosan, as a biomacromolecule, contains a large number of -NH2 and -OH groups on its polymer branches. The nucleation and growth of SiO2 on the poplar cell wall is directly related to the -NH2 groups on chitosan. -NH2 plays multiple roles in the biomimetic synthesis of SiO2: First, -NH2 can catalyze the hydrolysis of the organosilicon precursor TEOS, releasing alcohol to obtain a silanol-containing molecule (R3Si-OH), which then generates Si-O-Si bonds through a condensation reaction; second, -NH2 can also promote the aggregation and polymerization of negatively charged silicates to form SiO2 precipitates, such as... Figure 2 The mechanism diagram is shown in the figure. The EDS layering diagram of LSP shows that the Si element is uniformly distributed, with a content of 8.63% ( Figure 6 (G) This indicates that chitosan induces rapid silica deposition in poplar cell walls and pores. Chitosan and SiO2 synergistically form an organic-inorganic hybrid film on the poplar cell wall. The chitosan-SiO2 film not only enhances the strength of the poplar cell wall but also makes the bond between SiO2 and poplar more stable. In the study on the properties of gelatin-silica mineralized wood composites by Li et al. (2022), the uniform distribution of SiO2 on the wood cell wall was observed using SEM. This study further reveals the changes in microstructure and Si element distribution of multilayer self-assembled chitosan-SiO2 mineralized fast-growing wood composites. Compared with the study by Yang et al. (2021) on improving the interfacial strength of composites through multilayer self-assembly technology, this study uses some of the same technology to improve the microstructure of poplar and enhance the bond between inorganic nanoparticles and poplar. By combining the multilayer self-assembly method and the sol-gel method, uniform deposition of SiO2 on the poplar surface was achieved, and the characteristic changes in the SEM images of poplar after SiO2 mineralization treatment were clarified. Detailed EDX analysis confirmed the chemical bonding between SiO2 and the poplar cell wall, revealing the important role of this bonding in altering the microstructure of poplar.

[0114] 3. Conclusion

[0115] The limitations of traditional wood in terms of water resistance, flame retardancy, and mechanical properties restrict its application in a wider range of environmental conditions. This study successfully prepared a multilayer self-assembled chitosan-synergistic SiO2 mineralized fast-growing wood composite (LSP) using a biomimetic mineralization principle combined with a multilayer self-assembly method (LBL) and a sol-gel method. The preparation process is environmentally friendly, controllable, and convenient. The conclusions are as follows:

[0116] a. The oven-dry density and weight gain of the prepared LSP were significantly improved, indicating that the densification of poplar cell walls was successfully achieved. Its radial and tangential saturated water swelling rates and water absorption rates were significantly reduced, showing good dimensional stability and water resistance.

[0117] b. Infrared spectroscopy analysis confirmed that SiO2 formed Si-O-Si and Si-OC bonds with hydroxyl groups on the poplar cell wall, indicating the successful construction of an organic-inorganic hybrid structure. Scanning electron microscopy observed the uniform distribution of nanoscale SiO2 on the poplar cell wall, further confirming the tight bonding between the inorganic mineral and the organic matrix.

[0118] c. Thermogravimetric analysis (TGA) results show that the thermal stability of the LSP is significantly improved due to the deposition of SiO2 and the formation of an organic-inorganic hybrid structure. 5% T10% and T max The decrease in the value and the increase in the residual carbon rate at 800℃ demonstrate the positive effect of SiO2 mineralization on improving the thermal stability of poplar.

[0119] This application not only provides a new strategy for the high-value-added application of low-value fast-growing poplar, but also provides a scientific basis and technical support for the functional modification of biomass materials and the development of environmentally friendly materials.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for the production of a mineralized engineered wood composite material, characterized in that, The method comprises the following steps: (1) immersing untreated poplar in deionized water at normal temperature and pressure to remove impurities on the surface of the poplar; then taking out the poplar and drying it to absolute dryness for standby; then immersing the poplar in an alkali solution at normal temperature and pressure, and then washing the surface of the poplar with deionized water; (2) placing the treated poplar in a polycation solution for vacuum immersion, and washing the surface of the poplar; (3) placing the poplar immersed in the polycation solution into a polyanion solution for vacuum immersion, and washing the surface of the poplar; (4) then placing the sample into the polycation solution again for vacuum immersion, and washing the surface of the poplar; (5) preparing a precursor solution by mixing a silicon source with deionized water, adjusting the pH of the solution to 2-3, and then magnetically stirring, and then immersing the poplar treated in step (4) in the precursor solution under pressure; (6) taking out the poplar from the SiO2 precursor solution, washing the surface of the poplar with deionized water, and then placing it into an oven for drying to absolute dryness after air drying; (7) repeating steps (2), (3), (4), (5) and (6) several times to prepare a mineralized fast-growing wood composite material.

2. The method of producing a mineralized fast growing wood composite material according to claim 1, characterized in that, In step (1), the time for immersing in deionized water is 24 h.

3. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In step (1), the time for immersing in the alkali solution is 15 min, and the alkali solution is a NaOH solution with a mass fraction of 2%.

4. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In steps (2) and (4), the polycation solution is selected from one of chitosan, polydiallyldimethylammonium chloride, polyethyleneimine, and polyacrylamine hydrochloride, and the concentration of the polycation solution is 8 g·L -1 .

5. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In steps (2), (3) and (4), the specific conditions for vacuum immersion are as follows: the negative pressure is 0.1 MPa, the immersion time is 1 h, and the immersion temperature is 20℃.

6. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In step (3), the polyanion solution is selected from one of sodium polystyrene sulfonate, sodium phytate, polyacrylic acid, and sodium alginate, and the concentration of the polyanion solution is 5 g·L -1 .

7. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In step (5), the silicon source and deionized water are mixed at a mass ratio of 5:

1.

8. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In step (5), the time for magnetic stirring is 30 min.

9. The method of producing a mineralized engineered wood composite material according to claim 1, characterized in that, In step (5), the time for immersing in the precursor solution under pressure is 12 h, and the pressure is kept at 0.5 MPa.

10. A mineralized engineered wood composite material, characterized by, The mineralized fast-growing wood composite material prepared by the method of any one of claims 1-9. The mineralized fast-growing wood composite material prepared by the method of any one of claims 1-9.

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